SUMMARY

There are a number of ways the presence of water contributes to damage in asphalt and composite (asphalt surfaces on concrete) pavements. Being able to limit the damage to these pavement structures caused by the presence of water begins with an understanding of the sources of water. Starting with the surface layer, for example, water can enter the pavement structure through cracks, longitudinal paving joints, open-graded mixtures, and poorly consolidated asphalt layers. Water from the surface or outside the pavement structure (e.g., from shoulders or from beneath the pavement structure) can saturate and weaken aggregate base layers and subgrade soils. Moreover, pavement structures that restrict the positive flow of water away from the pavement section (due to such things as improper cross slopes, the buildup of materials or debris at the pavement edge, or the presence of a “bathtub” pavement cross section) can weaken pavement layers, leading to accelerated pavement damage and reduced pavement life. Finally, not adequately accounting for existing environmental conditions can also detract from pavement performance as a result of the presence of moisture. Examples of potentially adverse environmental effects include insufficient structural depth to account for freeze-thaw conditions, high water tables, perched water tables, or water trapped between poorly bonded or unbonded layers.

The damaging effects of moisture in asphalt and composite pavements includes increased susceptibility of the pavement materials to the presence of moisture and reduced strength of various pavement layers when wet or saturated. In a study conducted by Lu, Harvey, and Monismith (2007), a statistical analysis of condition surveys and field sampling results indicated that air void content, pavement structure, cumulative rainfall, asphalt mix type (dense-graded versus gap-graded rubber modified), anti-strip additive (lime or liquid), and pavement age are all variables that have a significant effect on the amount of pavement damage caused by water; the study concluded that high air void asphalt mixtures not only allowed more water to infiltrate a pavement, such mixtures also resulted in significantly reduced fatigue life in wet conditions. It was observed that mixtures with less-than-optimum asphalt binder contents resulted in lower moisture resistance under repeated loading.

Studies have also shown that the presence of water in pavement layers adversely impacts the bearing capacity and service life of both asphalt and concrete pavements (Grover and Veeraragavan 2010; Ceylan et al. 2013). In addition, in cold climates, the detrimental effects of water in pavement layers are amplified due to potential damage from freeze-thaw effects. And, for composite pavement structures consisting of an asphalt surface on a concrete pavement, the infiltration of deicing chemicals could contribute to the accelerated deterioration of the underlying concrete slab.

Recognizing that there is no single source of information that addresses issues and techniques for limiting pavement damage caused by water, NCHRP Project 01-54, “Guidelines for Limiting Damage to Flexible and Composite Pavements Due to the Presence of Water,” was initiated with the following objectives:

• Develop guidelines detailing strategies to limit damage to flexible and composite pavements due to the presence of water.
• Assemble a 1-day training course for practicing engineers on the use of the guidelines.

• Develop a stand-alone web-based application to provide easy access to the guidelines content.
• Prepare a webinar covering the project content.

In response to those objectives, the following primary products were developed under NCHRP Project 01-54:

• A Guidelines document covering a broad set of topics related to drainage evaluation, assessment, and improvement:
  • – Sources of water in pavement structures.
  • – Moisture-related distress mechanisms.
  • – Pavement design features to address the effects of moisture.
  • – Types of materials and material selection to mitigate moisture impacts.
  • – Constructing pavements to limit moisture-related damage.
  • – Maintenance and preservation strategies.
  • – Rehabilitation strategies.

This stand-alone document also contains several key appendixes, including standard drainage plans, specifications, and selected agency fact sheets.

• The PowerPoint presentation materials for a 90-minute webinar on limiting moisture damage in asphalt and composite pavement structures.
• A 1-day training course to provide practicing engineers with a detailed introduction to the Guidelines. The course materials include PowerPoint slides, an Instructor Guide, and a Participant Workbook, all of which were developed in general accordance with the protocols used by the National Highway Institute (NHI) for consistency purposes only.
• A companion web-based application (DRAIN) for easy access to the technical content summarized in the Guidelines. By answering a series of questions about a given project, the application provides users with an indication of whether moisture will impact the performance of their pavement projects and where they can access additional information to understand the impacts and identify solutions.

It should be pointed out that the recommendations in the Guidelines document are neither new nor unique. The value of the document lies in the fact that in a single source they present successful practices that have been used by highway agencies nationwide in minimizing the adverse effects of moisture on flexible and composite pavement structures at all of the stages of a pavement’s life, from design to construction, maintenance and preservation, and rehabilitation. The training materials and application further facilitate access to this useful information.